In the post, Arma 3 project lead Joris-Jan van 't Land said, "One of the steps in this plan has been to select Valve's
Steam as
our primary platform. Not only is Arma 3 PC-exclusive, but now we have decided
to make it Steam-exclusive as well. Since we expect this will upset some of our
fans, I'd like to take the time to honestly explain our motivations."

He
went on to explain the company's reasoning at some length, which you can read
on the full blog post. However, to summarize: The company has a good working
relationship with Steam, and many of the service's features regarding things
like patching and DLC make Bohemia's job of supporting the game post-launch
easier and less expensive. By going only with Steam, it will only have to worry
about supporting one version of the game and one distribution channel, allowing
Bohemia's team to focus on what it does best: developing the game itself.

He
also went on to talk about Steams DRM management - which is perhaps the aspect
of the decision that Bohemia expecting pushback from fans on.

"Think
of it what you want, but piracy is affecting us as a business," he said. "However,
Bohemia Interactive has tried to grow with the evolution of the Internet,
rather than to fight it. We have removed intrusive Digital Rights Management
(DRM) from our games several months after release, but cannot afford to launch
without such technologies. We strongly believe the best anti-piracy comes from
offering valuable online services that people are willing to invest in.
Supporting that philosophy: we saw we could not deliver in-house solutions on
time, but could take Steam's and expand upon them. It will be possible to run Steam in Offline mode, and still play
the game (with the exception of online services obviously,
including multiplayer itself)."

He
also said that boxed copies of Arma 3 will be available, which might be either
Steam codes in a package of some sort or DVDs which contain data to speed
installation. However, all copies of the game must be run and updated through
Steam.

He
also stated that the decision was made because Bohemia felt making Arma 3
exclusive to Steam was the only way the company would be able to release the
game in 2013.